Human Brain Anatomy: No Bones, Just Soft Tissue Protected by the Skull

The human brain contains no bones. It is a soft, gelatinous organ (≈1.3–1.4 kg) composed of:

• Cerebrum (cerebral hemispheres): higher cognition, voluntary motor, sensory.
• Cerebellum: coordination, balance, motor learning.
• Brainstem (midbrain, pons, medulla): vital centers (respiratory, cardiac), cranial nerves.

Protective Layers

1. Skull (cranium): Rigid bony enclosure.
2. Meninges: Dura mater (tough), arachnoid (web-like), pia mater (delicate, adherent).
3. Cerebrospinal fluid (CSF): Circulates in subarachnoid space and ventricles; buoyancy, cushioning, waste clearance.

Composition

• ~75% water
• ~10% lipids (myelin)
• ~8% proteins
• ~2% carbohydrates, salts, trace elements
• ~86 billion neurons + ~85 billion glia

Clinical Relevance

Trauma can cause contusions, hemorrhages (epidural, subdural, subarachnoid, intraparenchymal) without skull fracture. The brain's softness makes it vulnerable to acceleration-deceleration forces.